Glycoprotein hormones and free subunits are secreted by the pituitary, placenta, and certain tumors both in vivo and in vitro. Normal cells synthesize alpha subunit in excess of beta subunit, but the production of the latter is preferentially regulated by various hormones. Pituitary and other tumors may secrete alpha in greater excess and may be autonomous to normal regulatory factors. Biosynthetic studies have shown that the alpha and beta subunits are independently synthesized initially as precursor forms that are glycosylated before combining to form active hormone. Only glycosylated hormones and free alpha are secreted.